EP0896739A1

EP0896739A1 - Diode-addressed colour display with lanthanoid phosphors

Info

Publication number: EP0896739A1
Application number: EP98904317A
Authority: EP
Inventors: Herbert Boerner; Thomas JÜSTEL; Hans Nikol
Original assignee: Philips Corporate Intellectual Property GmbH; Philips Patentverwaltung GmbH; Koninklijke Philips Electronics NV
Current assignee: Philips Intellectual Property and Standards GmbH; Koninklijke Philips NV
Priority date: 1997-03-04
Filing date: 1998-03-03
Publication date: 1999-02-17
Also published as: WO1998039807A1

Abstract

The invention relates to a diode-addressed colour display comprising a UV diode and a phosphor of the composition LnL3X2, where Ln = Eu?3+, Tb3+, Tm3+, Dys3+, Sm3+¿, L = 4-R-4'-benzophene carboxylic acid where R = phenyl, benzyl, CH¿3?, CF3, C2H5, F, Cl, OCH3, CH3CO; 4-R-4'-benzophenone acetylacetonate where R = phenyl, benzyl, CH3, CF3, C2H5, F, Cl, OCH3, CH3CO; 4-acetophenone carboxylic acid, 4-trifluoroacetophenone carboxylic acid, 4-acetophenone acetylacetonate or 4-trifluoroacetophenone acetylacetonate and X = 1/2 phenanthroline, 1/2 diphenyl phenanthroline, 1/2 4-Cl-phenanthroline, 1/2 bipyridine, 1/2 ethylne diamine, triphenylphosphine oxide, trimethylphosphine oxide, triethylphosphine oxide, 1/2 diethylene glycol dimethyl ether or ethanol.

Description

Diode-addressed color display with lanthanide phosphors.

The invention relates to a diode-addressed color display with a UV diode and a phosphor for illuminated displays, lights, solid-state image intensifiers, screens and monitors and others.

Color displays for illuminated displays, luminaires, solid state amplifiers, screens and monitors are intended to reproduce color images in true color. Technically, this object is achieved in that the entire color information of a colored image is represented by information about the three primary colors red, green and blue. Additive color mixing can be used to produce any color or white from the three primary colors. This principle is used both by the conventional color television set with a tube from Braunschweig and by the various flat screen technologies such as plasma screens,

Electroluminescent screen and LCD displays. There are also color displays on the market in which the triple color red, green, blue is generated by diode arrays with red, green and blue emitting semiconductor diodes. However, the color-true image reproduction, in particular the color-pure reproduction of green and blue, is problematic. The development of UV-emitting semiconductor diodes has expanded the possibilities for true-color image reproduction for diode-addressed color displays, since theoretically any color of visible light can be generated from UV light. For this purpose, phosphors are used which absorb the UV light and emit it again with a wavelength in the visible range. For this conversion of the UV light into the visible range, it is known to use inorganic pigments as phosphors. For example, it's off

Jpn.J.Appl.Phys. Vol.35 (1996) pp.L838-L839 known to use ZnS: Ag, ZnS: Cu.Al and ZnCdS: Ag as phosphors for converting the UV light from the UV diode in a fluorescent color display. Although these and other conventional phosphors such as Y ₂ O ₃ : Eu have a high quantum yield, their absorption in the near UV range in which the UV diodes emit is very low.

It is therefore an object of the present invention to provide a diode-addressed color display with a UV diode and a phosphor, the phosphor of which has a high quantum efficiency and a high extinction coefficient in the near UV wavelength range and a color-true image reproduction

CONFIRMATION COPY allowed.

According to the invention the object is achieved by a diode-addressed color display with a UV diode and a phosphor of the composition LnL ^ X ;, with Ln = Eu ^{3 +} , Tb ⁺ , Th ^{3 +} , Dys ^{3 +} , Sm ^{3 +} , L = 4- R-4'-benzophenone carboxylic acid with R = phenyl, benzyl, CH ₃ , CF ₃ , C ₂ H ₅ , F, Cl, OCH ₃ , CH ₃ CO; 4-R-4'-benzophenone acetylacetonate with R = phenyl, benzyl, CH ₃ , CF ₃ , C ₂ H ₅ , F, Cl, OCH ₃ , CH ₃ CO; 4-acetophenone carboxylic acid. , 4- trifluoroacetophenone carboxylic acid, 4-acetophenone acetylacetonate or 4- trifloracetophenone acetylacetonate and X = 1/2 phenanthroline, 1/2 diphenylphenanthroline, 1/2 4-Cl-phenanthroline, 1/2 bipyridine, 1/2 ethylenediamine, triphenylphosphine oxide, trimethylphosphine oxide, trimethylphosphine oxide, 1/2 diethylene glycol dimethyl ether (diglyme) or ethanol.

Such a color display is characterized by a high intrinsic emission quantum yield and a ligand-centered absorption in the near UV and the short-wave visible range between 320 and 450 nm with high extinction coefficients. The UV absorption has its maximum at 390 to 320 nm. According to photophysical considerations, these two phosphor properties are actually mutually exclusive. Surprisingly, however, it has been shown that phosphors of the composition LnL ₃ X ₂ meet both criteria. The phosphors according to the invention with the "antenna molecules" L, which contain benzophenone or acetophenone as structural elements, have many times higher absorptions than classic phosphors. A variation of the ligands L allows the almost linear, independent introduction of high absorptions at different wavelengths into the lanthanoid compounds. Concentration quenching, a general problem with classic phosphors with a high activator concentration, is not observed with the phosphors according to the invention. The phosphors according to the invention are molecular compounds and therefore generally readily soluble in polar organic solvents. Their properties can therefore be easily examined in solution and the test results can be transferred to the solid state. The solubility in organic solvents also allows new design concepts for diode-addressed color displays. In the context of the present invention, it is preferred that the diode-addressed color display comprises a transparent polymeric coating which contains the phosphorus of the composition LnL ₃ X ₂ in solid solution. The coating is transparent because the light is not scattered on the dissolved phosphor particles.

The invention is illustrated below using three exemplary embodiments explained further.

A diode-addressed color display according to the invention comprises a UV-emitting diode as an excitation source for UV radiation and a phosphor of the composition LnL ₃ X ₂ with Ln = Eu ^{3 +} , Tb ^{3 +} , Tm ^{3 +} , Dys ^{3 +} , Sm ^{3 +} , L = 4-R-4'-benzophenone carboxylic acid with R = phenyl, benzyl, CH ₃ , CF ₃ , C ₂ H ₅ , F, Cl, OCH ₃ , CH ₃ CO; 4-R-4Xbenzophenone acetylacetonate with R = phenyl, benzyl, CH ₃ , CF ₃ , C ₂ H ₅ , F, Cl, OCH ₃ , CH ₃ CO; 4-acetophenone carboxylic acid, 4-trifluoroacetophenone carboxylic acid, 4-acetophenone acetylacetonate or 4-trifloroacetophenone acetylacetonate and X = 1/2 phenanthroline, 1/2 diphenylphenanthroline, 1/2 4-Cl-phenanthroline, 1/2 bipyridine, 1/2 ethylenediamine, triphenylphosphine, triphenylphosphine , Triethylphosphine oxide, 1/2 diethylene glycol dimethyl ether (diglyme) or ethanol. The phosphors containing europium or samarium convert the UV radiation into visible red light. The terbium-containing phosphor converts to green light, the thulium-containing to blue and the dysprosium-containing to blue-yellow mixed light. In the simplest case, a color display according to the invention consists of the

UV diode and a transparent coating applied to it, which contains the phosphorus. The transparent coating can contain, for example, the phosphorus in a solid solution in a transparent matrix made of polyacrylate, polystyrene, epoxy resin or another polymer. As mass products, LEDs are usually cast in epoxy housings, with the cast-on lens made of epoxy resin serving to improve the coupling out of the light from the diode. In this embodiment, the phosphor can be applied as a contact layer between the actual diode and the epoxy resin dome. It can also be applied as a coating on the outside of the epoxy resin dome. According to another embodiment, the phosphorus is mixed with the epoxy resin and forms a solid solution with it.

Large, two-dimensional displays can be easily manufactured by combining a diode array with the phosphor according to the invention. For example, the diode array can be covered by a glass plate which is printed with fluorescent triplets, each with a red, green and blue glowing dot. The red glowing dot contains LnL ₃ X ₂ as phosphor. The UV diode is in particular a UV diode made of InGaN or GaN and has its emission maximum between 370 and 410 nm with a half width FWHM <50 nm.

The phosphors according to the invention have the composition LnL ₃ X ₂ with Ln = Eu ^{3 +} , Tb ^{3 +} , Tm ^{3 +} , Dys ^{3 +} , Sm ^{3 +} , L = 4-R-4 ^X benzophenonecarboxylic acid with R = phenyl, benzyl, CH ₃ , CF ₃ , C ₂ H ₅ , F, Cl, OCH ₃ , CH ₃ CO; 4-R-4'-benzophenone acetyl acetonate with R = phenyl, benzyl, CH ₃ , CF ₃ , C ₂ H ₅ , F, Cl, OCH ₃ , CH ₃ CO; 4- acetophenone carboxylic acid, 4-trifluoroacetophenone carboxylic acid, 4-acetophenone acetylacetonate or 4-trifloroacetophenone acetylacetonate and X = 1/2 phenanthroline, 1/2

Diphenylphenanthiolin, 1/2 4-Cl-phenanthroline, 1/2 bipyridine, 1/2 ethylenediamine, triphenylphosphine oxide, trimethylphosphine oxide, triethylphosphine oxide, 1/2 diethylene glycol dimethyl ether (diglyme) or ethanol. These complex coordination compounds of the lanthanoids europium, terbium, thulium, dysprosium and samarium contain Eu ^{3 +} , Tb ^{3 +} , Tm ^{3 +} , Dys ^{3 +} and Sm ^{3 +} as the metal center, benzophenone-4-carboxylic acid or its derivatives or benzophenone-4 -acety lacetonate or its derivatives as charged ligands and phenanthroline, 1/2 diphenylphenanthroline, 1/2 4-Cl-phenanthroline, 1/2 bipyridine, 1/2 ethylenediamine, triphenylphosphine oxide, trimethylphosphine oxide, triethylphosphine oxide, 1/2 diethylene glycol dimethyl ether ( diglyme) or ethanol as neutral ligands. These coordination compounds have strong optical intraligand transitions and, in addition to absorbing the chelate ligands, are also effective as light antennas. The primary excitation by UV radiation leads to a ligand-centered excited state, the energy of which is transferred to the lanthanide ion in a subsequent step and leads to light emission there. In these compounds, the original absorption properties of the ligands and the

Interligand interactions are weak. The coordinative saturation of the lanthanide prevents the tendency to polymerize of the compounds, which are therefore mononuclear. In contrast to the phosphors according to the prior art, molecular phosphors are therefore composed of host lattices doped with activator ions.

Embodiment 1

To prepare Tb (C ₁₄ H ₉ O ₃ ) ₃ (C ₂ H ₅ OH) ₂ , 1.0 mmol of TbCl ₃ aq in 10 ml of ethanol become a solution of 3.0 mmol of benzophenone-4-carboxylic acid (R = H) in 70 ml Ethanol is added, then 3.0 mmol NaOCH _{3 are} added and the mixture is stirred at 60 ° C. for 2 h. The white precipitate is filtered off and washed with methanol and dried.

When excited with 254 nm radiation, a quantum yield of 70% was measured. It can be seen from the excitation spectrum that the phosphor can be excited up to 375 nm. Embodiment 2

To produce Tb (C ₁₄ H ₉ θ ₃ ) ₃ [(C ₆ H ₅ ) ₃ PO] ₂ , 1.0 mmol

Tb (C ₁₄ H ₉ O ₃ ) ₃ (C ₂ H ₅ OH) ₂ with 2.3 mmol TPPO in 1,2-dichloroethane at 50 ° C for 2 h. The previously insoluble powder slowly dissolves. The solution obtained in this way can be used directly after filtration and can be used to add a polymer such as polyacrylate or polystyrene to a thin transparent coating of the UV diode.

When excited with 254 nm radiation, a quantum yield of 45% was measured. It can be seen from the excitation spectrum that the phosphor can be excited up to 380 nm.

Embodiment 3

For the production of Eu (C ₁₄ H ₉ O ₃ ) ₃ (C ₁₂ H ₈ N ₂ ) ₂ , 1.0 mmol EuCl ₃ aq in 10 ml ethanol become a solution of 3.0 mmol benzophenone-4-carboxylic acid (R = H) in 70 ml of ethanol. Then 3.0 mmol NaOCH _{3 are} added and the mixture is stirred at 60 ° C. for 2 h. The white precipitate is filtered off and washed with methanol and dried. Then 1 mmol of the product is dissolved together with 1 mmol of 1,10-phenanthroline in 50 ml of ethanol and the suspension is boiled under reflux for 2 h. The complex formed is suction filtered and washed with ethanol and dried. When excited with 254 nm radiation, a quantum yield of 73% was measured. It can be seen from the excitation spectrum that the phosphor can be excited up to 375 nm.

Claims

PATENT CLAIMS

1. Diode-addressed color display with a UV diode and a phosphor of the composition LnL ₃ X ₂ with Ln = Eu ^{3 +} , Tb ^{3 +} , Tm ^{3 +} , Dys ^{3 +} , Sm ⁺ , L = 4-R-4'-benzophenonecarboxylic acid with R = phenyl, benzyl, CH ₃ , CF ₃ , C ₂ H ₅ , F, Cl, OCH ₃ , CH ₃ CO; 4-R-4'-benzophenone acetylacetonate with R = phenyl, benzyl, CH ₃ , CF ₃ , C ₂ H ₅ , F, Cl, OCH ₃ , CH ₃ CO; 4-acetophenone carboxylic acid, 4-trifluoroacetophenone carboxylic acid, 4-

Acetophenone acety lacetonate or 4-trifloroacetophenone acety lacetonate and X = 1/2 phenanthroline, 1/2 diphenylphenanthroline, 1/2 4-Cl-phenanthroline, 1/2 bipyridine, 1/2 ethylenediamine, triphenylphosphine oxide, trimethylphosphine oxide, triethylphosphine oxide, 1/2 diethylene glycol Dimethyl ether (diglyme) or ethanol.

2. Diode-addressed color display according to claim 1, characterized. that the diode-addressed color display comprises a transparent polymeric coating which contains the phosphorus of the composition LnL ₃ X ₂ in solid solution.